When the beliefs of any religion
are good or bad, true or false, then the religion will also be good or bad, true or false. That is, the truth or falsehood of a religion is related to its beliefs; the goodness or badness of its rulings has no part in this.
Because if it were related to rulings, the rulings are also very numerous; it would be necessary to investigate every ruling, and the process of inquiry is not without difficulty.
Yes, if the truth of a religion is linked to beliefs, it is appropriate. This is because, firstly, a belief is a type of news.
If the belief is correct, it will be said that it corresponds to reality and is a true statement,
and if it is wrong, it will be said that it is a false statement.
Since in every religion there are only a few beliefs, it is not such a long and broad story that investigation would be difficult.
Therefore, it is better for the truth of a religion to be related to beliefs rather than rulings.
The Truth of Islam in Terms of Beliefs
If Islam is viewed from the perspective of beliefs,
the religion of Islam appears superior to all other religions.
Accordingly,
the first belief of the people of Islam
upon which the foundation of Islam is laid, is this:
(La ilaha illallah Muhammadur Rasulullah sallallahu alaihi wasallam), which means that there is no one worthy of worship except Allah Almighty, and Hazrat Muhammad (sallallahu alaihi wasallam) is the messenger sent by Allah Almighty.
The first part of this Kalima—La ilaha illallah—
the summary of which is Tawheed.
All religions do not deny this; rather, in every religion, a form of Tawheed exists to some degree,
such as the ignorant of Arabia and the Christians.
The ignorant of Arabia used to worship thousands of idols,
but they considered only one God to be the Creator of the earth and the heavens. Accordingly, the Holy Quran speaks of their condition thus:
Wa la-in sa'altahum man khalaqas-samawati wal-arda layaqulunnallah
That if you ask them who created the heavens and the earths, they would say, "Allah."
As for the Christians, although they are at the top in Shirk. This is because they associate partners in the Essence—that is, they believe in three gods at the level of the Essence, such that according to them there are three gods in reality, and those three are also one in reality. Therefore, even among them, the hem of Tawheed was not let go from their hands.
In short, it is known from this that no one is a denier of Tawheed; rather, the fundamental principle for everyone is Tawheed itself. And when Tawheed is accepted and established as the principle for everyone, then those things which are against Tawheed will themselves be wrong. That is, Shirk, idol worship, and the multiplicity of deities will automatically become wrong...
(Majmu'a Rasail-e-Qasmiya, Mela-e-Khuda Shinasi, pp. 90 to 92)